The move was hardly a surprise; Gingrich has spent months raising money, assembling a campaign team and visiting early primary states. He also quietly opened a campaign headquarters in Atlanta, and had long been scheduled to address the Georgia Republican Party Convention on Friday in Macon, Ga. Aides say that will be his first speech as a full-fledged candidate.

Gingrich, 67, enters a GOP field that's far from fully formed; no less than a dozen Republicans are weighing bids and only a few have taken steps toward candidacies. It's a crop of candidates that has many in the Republican Party yearning for more options as they seek the strongest candidate to take on President Barack Obama in 2012.

Gingrich's entry into the race marks a comeback attempt by the former Georgia congressman who stepped down from the House after four tumultuous years as speaker in the 1990s.

He led the GOP to its first majority in the House in 40 years, spearheading the Republican revolution in the 1994 elections. A spending fight between Gingrich and President Bill Clinton led to federal government shutdowns in 1995 and 1996. He faced ethics questions during part of his tenure, and left Congress in 1999. Since then, he's traveled the world speaking on issues from health care to foreign affairs, built a lucrative network of nonprofit and business ventures, and written a steady stream of books.

In recent months as he geared up for a run, Gingrich has lambasted Obama's federal health law and has criticized the Democrat's foreign policy as "clueless."

The twice-divorced Gingrich also has been working to make inroads with social conservatives critical to the GOP primary base, highlighting his conversion to Catholicism after marrying his third wife, Callista. She has figured prominently in campaign appearances in the months since Gingrich made clear he was considering a run.

Although he's lived in northern Virginia for more than a decade, the Pennsylvania-born Gingrich has also been playing up his Georgia roots. He taught college in Georgia and was a longtime congressman from suburban Atlanta, helping build the Republican Party in the state dominated at the time by Democrats.